Pump-off controllers have been commonly used in the upstream oil and gas industry to control the pumping of oil and gas wells, particularly on fluid producing wells wherein the pumping equipment is capable of lifting more fluid from the wellbore than the formation is capable of producing into the wellbore. The most common prime mover on a pumping unit is an electrical motor. To control the pumping of a well, the electric motor may be stopped, started, sped up or slowed down.
A pumping system on a well may include a beam type pumping unit, a prime mover, a power source, a motor control panel, a pump-off controller (POC) and POC control panel, rods, production tubing, downhole pump and a pumping type wellhead assembly. At some point in the life of a pumping system, the pumping system capacity may substantially exceed the productivity of the well. When the outflow capacity of the pumping equipment or artificial lift equipment exceeds the inflow capacity of the reservoir to the well, to prevent excessive wear and damage to the pumping equipment due to the partially filled pump and to save electricity, a well may be pumped for a first interval of time and then shut down for a second interval of time to allow the wellbore to fill with fluid. One method of effecting this interval pumping technique is with a time clock type device. When the fluid column in the wellbore builds, the inflow from the reservoir slows and eventually ceases when the pressure at the formation face in the wellbore equals the formation pressure. It is then desirable to turn the pumping unit back on to pump the produced fluid from the wellbore and then repeat the process.
In order to maximize the production rate from a well, there is usually an optimum time at which to turn the pumping unit back on prior to complete cessation of inflow. It may be difficult to determine exactly when all of the fluid has been pumped from the wellbore in order to timely shut down the pumping unit to avoid excessive equipment wear and energy consumption. Also, as wells are produced, the inflow conditions may change over time, particularly early in the life of a new well, or when utilizing a secondary or tertiary recovery mechanism such as waterflooding. For these and other reasons, pump-off controllers are typically employed on pumping units to improve the efficiency, productivity and life of the pumping system.
Pump-off controllers (POC) typically operate to determine the appropriate time to turn a pumping unit on, when to turn it off, how long to wait before turning the unit back on and then restarting the unit to repeat the cycle. They may also monitor pumping parameters for fault conditions. POC's may function by measuring the changes or absolute values of time cycles such as stroke speed, loading on various components such as the polished rod, electrical system changes such as motor current and/or a combination of other measurements related to these components. Other pump-off controllers may function to control the pumping unit by comparing the integrated area in the curve of a plot of predicted load vs. polished rod position, to the integrated area in the curve of a plot of measured load vs. polished rod position.
POC measuring and data inputs and outputs are conventionally hard wired to the pumping unit motor control panel, with the POC typically residing in a separate control panel. Analog and/or digital transducers or measuring end devices may be connected on one end to the pumping unit and on the other end to the motor control panel and/or connected directly to the POC panel. The POC may be powered by an electric line from the motor control panel running to the pump-off control panel or it may be powered by a solar panel. POCs also typically have a battery for back-up power in the event of primary electrical power failure.
Typically, electrical components in a pumping system are connected with electrically conductive wire. A drawback to this type connectivity is that when transients, induced currents, switching surges, power feeder surges, over-loads, short circuits, static discharges or lightening strikes hit one component in the system, all components are at risk of damage from the current surge. To combat this problem, lightening protection, surge suppression, fuses, over-load switches and other protection equipment may be employed. These protection systems are not fool-proof in that a misapplication or improper design may result in little or no protection and thereby result in damaged or destroyed devices. Poor electrical grounding may also result in ineffective device protection.
Damage to circuitry in a POC may result in relatively expensive costs due to direct loss and replacement of equipment. Additional losses may be incurred due to lost production from downtime due to the equipment failures and/or operation of partially filled pumping equipment resulting in damaged pumping equipment and wasted energy.
An improved method of isolating a POC is desired in order to reduce the risk of damage or destruction of POC's and related equipment. The disadvantages of prior art are overcome by the present invention and an improved method of connecting and protecting POC installations and related equipment are hereinafter disclosed.